Automatic slack adjuster



Sept' 22, 1936. A. B. scHuLTz- 2,055,182

AUTOMATI'C SLACK ADJUSTER `Filed June 6, 1932 l 4 49 3 16 /6 ,f1 -f as @y Uff/ff 423 ##119 15 ATTORNEY.'

Patented Sept.2`2,l

.UNI-TED* sTA'Tas PATENT oFFlcE n ApplicationJune 6, 1932, Serial No. 615,578 s claims. (c1. iss-19s) This `invention relates to improvements in liquid pressure mechanisms. In itsbroader aspects, the invention maybe applied to various types of hydraulic devices, in which the actuated member is of a type whichl acts against a positive stop and is retracted when pressure is released. The embodiment specifically referred to herein `discloses its application to a hydraulic braking system for selfepropelled vehicles.

, of said stroke to compensate for brake surface The principal object of the invention is to provide a device which will automatically control the distance of retraction of theactuated memberwhen the actuating fluid pressure is released.

Another object of the -invention is to provide a device which will automatically adjust the fluid volume in hydraulic brake lines to compensate for the variations caused by the change of temperature, the loss of iiuid, and the like.

Another object of the invention is to provide an adjustment for hydraulic brakes which will automatically take up excessive brake shoe clearances l caused by Worn brake linings.

Another object of the invention is to provide a device which will at all times maintain a positive pressure inthe fluid lines and eliminate the possibility of bubbles entering the fluid lines yand causing the objectionable soft pedal action familiar to the users of hydraulic brakes.

Another object of .the invention is to provide.

a device which will increase the power and efflciency of the braking system by allowing the full stroke of the actuating member to be used for work instead of allocating a certain portion scription proceeds, will be more readily understood from'an examination of the followingrspcification, reference being had to the accompanying drawing, in which: y I

Fig. 1 is a plan view in outline of a braking system of an automotive vehicle in which my invention is embodied.

Fig. 2 is an enlargedA view, partly ln section,

showing my inventioninparallel as an integral part of the'compressor of a hydraulic braking system.

Fig. 3 is an enlarged view, partlyA in section, illustrating the position assumed by the reciprocating member when the brake pedal vand compressor piston are at rest.

Fig. 4 is an enlarged view, vpartly in section, illustrating the position assumed by the reciprocating member when a uid line to the wheels is broken. f n

Fig. 5 is an enlarged view, partly in section, of a modified form of my invention illustrating the useof a double acting spring instead of two separate springs for maintaining. the reciprocating member in its neutral position.

Fig. 6 is an enlarged view, partly in section, of a modified lform of my invention illustrating the use of a tight fitting reciprocating member with a separate by-pass in the cylinder wall.

Referring now to the drawing,` it will be seen that this automatic control device, embodying my invention, is illustrated as being used in connection with a hydraulic braking system for automobiles, but it will be apparent to those skilled in the art that it might readily be used in connection with any fluid system in which it is necessary or desirable to have a uniform reciprocating movement of a iiuid actuated member.

In the drawing, 1 represents a set of automotive vehicle brakes operated by pressure exerted upon a foot pedal 8, which in turn actuates a iluid compressor 9, contained in housing I0,

which said compressor in turn transmits Jpressure to the brakes 'l through the automatic control members I'I and the fluid lines I2.

\.- 'I'he automatic control member II, in which resides the embodiment of my invention, comprises a cylinder I3 having a bore of suitable diameter and length, and preferably made with a fixed head I4 and a removable head I5'.

latter is provided with an externallythreaded The shoulder adapted to engage internal threads on the cylinder I3. A gasket I6, of any suitable material, is interposed between theends of the cyl- Ainder walls I3 and the removable head I5.

disposed near its inner terminus. The longitudinal passageway I1 has a similar annular recess 22 near its inner terminus. l

- A full floating reciprocating member 23 iscar- The fluid lines I2 are secured tothe 'ried in the cylinder I3. This reciprocating mem'- 55 ber 23 is loosely fltted in said cylinder I3 with sufficient clearance to allow fluid to by-pass it. The reciprocating member 23 is maintained in a predetermined intermediate position by means of springs 24 and 25 which are interposed .between the faces 26 and 2Iof the reciprocating member 23 and the cylinder heads I4 and I5 respectively.

The reciprocating member 23 is provided at its ends with projections 28 and 29 of such peripherial contour as will allow their engagement with the annular recesses 2I and 22.

The operation of the device is as follows:

'When the system is fllled with fluid and pressure is applied to the fluid in the compressor 9, this pressure is transmitted through the passageway I8 into the cylinder I3, thereby causing. the reciprocating member 23 to be displaced in the same direction as the moving fluid. In this-op eration the reciprocating member will move with the liquid until the fluid pressures in the compressor 9, the passageways I'I and I8, and the fluid lines I2 become the same, at which time fluid flow to the brakes ceases.' During this operation flow of fluid past the loosely fitting piston will be negligible, due to the small element of time required for the operation. When that condition is arrived at, the reciprocating member 23 should be in the position, as shown in Fig. 2. at which position springs 24 and 25 are under equal compression. Itis obvious that if the reciprocating member 23 be then displaced, either to the 'right or left from itsneutral position, as shown in Fig. 2, it will tend to return immediately to its neutral position under the influence of the difference in spring compressions set up by such displacement. Because of thedifference in the spring compressions liquid will then flow around the reciprocating member 23 toward the side of lesserpressure until the spring compressions again become equal, at which stage the reciprocating member 23 will again resume its lneutral position.

When the brake pedal 8 is released the uid pressure in the compressor 9 and the passageway I8 is reduced from approximately two hundred pounds per square inch to practically zero. This causes the fluid in the brakes 'I and the passage-way I2, which is under a pressure of from ten to twenty pounds per square inch caused by the customary brake shoe pulled back springs (not shown), to rush towards the passage-Way I'I and back into the compressor. 9. As the fluid moves towards the compressor 9 it carries piston 23 along with it for the reason that the fluid is unable to pass around the piston 23 fast enough to permit the piston 23 to remain stationary. This will be more readily comprehended when it is understood that the springs 24 and 25, which are of practically the same strength, have a resistance of only a fraction of an ounce when fully compressed, whereas the fluid trying to get by the piston 23 has a forceof from afour to five pounds. Thus the piston 23 is rushed towards the seat 22, which it quickly contacts and makes a fluid tight seal, as shown in Fig. 3, in which position it remains until the brakes are again applied.

Although thev pressure in all partsof the cylinder I3 tends to become equal because of the loose fit of the piston ,23, there is still a hydraulic pressure-exerted upon the piston 23 sumcient to hold the piston 23 against the seat 22.` That pressure represents the differential in pressures acting upon the piston from each end. In Fig. 3 the pressure actingon the left'end'ofithe piston isfrom ten to twenty pounds per square inch over the`l entire area, and on the right end of the piston 23 the pressure is the same over the entire area except that portion which is in the recess 22. On the latter area the pressure is practically zero, as it will be remembered the pressure ii the passage-way I1 was reduced to almost nothing when the brake pedal B was released. It will also be remembered that the springs 24 and 25 are comparatively weak, but of equal strength. It is, therefore, the difference in pressures acting upon an area equal to the area of the passageway I1 that overcomes the resistance of the spring 24' and causes thepiston 23 to remain seated.

When the piston 23 seats in recess 22 the flow of fluid from the brakes 1 immediately ceases. As the movement of the piston 23 from the neutral to the seating position, as shown in Fig. 3, is almost instantaneous, very little of the fluid will have time to pass around the piston 23 before the latter is seated, so that the volume swept by the movement of the piston 23 will be equal to the volume drawn from the brake cylinder. As the piston 23 centers itself, as shown in Fig. 2, upon` each application of the brake it is apparent that the brake shoes will contract to the same clearance each time the brakes are released. Each time the brakes are subsequently applied, the travel of the brake pedal will be the same, so it is apparent that there will result an automatic adjustment of the brake shoe clearance upon each application and release of the brakes.

In a normal operation, then, it will be seen that the piston 23 will move from its position, as shown in Fig. 3, to the position, as shown in Fig. 2, when the brakes are fully applied, and

will immediately return to the position of rest when the braking pressure is released. If, then, before the brakes are next applied the volume of fluid in the brakes and fluid lines I2 has decreased, resulting in an increased brake shoe clearance, it is apparent that when braking pressure actuates the reciprocating member 23 it will tend to move said member 23 beyond the neutral position until there is no longer a flow of liquid in that direction. When such condition is arrived at, the pressures on both sides-of the reciprocating member 23 will then be equal, except insofar as affected by the pressuresexerted on the reciprocating member 23 by the springs 24 and 25. In this position the compression of spring 25 will be greater than the compression of the spring 24, so it is obvious that there would be a flow of liquid past the reciprocating member 23 until the pressures on both sides of said member are equal, at which stage the reciprocating member 23 will again resume its neutral position, as shown in Fig. 2.

If, on the other hand, before the brakes are next applied, the volume of fluid in the brakes and fluid lines I2 has increased, resulting in a decreased brake shoe clearance, it is apparent that when braking pressure actuates the reciprocating member 23, it will move said member 23 to a po-` sitionshort of the neutral position, inasmuch as the brake shoes will make contact and stop the flow of fluid before the reciprocating member 23 reaches its aforesaid neutral position. When such static condition is arrived at there will be no flow of fluid in or out of ports I1 and I9 and the fluid pressure on both sides of the reciprocating member 23 will be equal, except insofar as affected by the slight pressure exerted on the y reciprocating member 23 bythe springs 24 and 25.- In this positionshort of neutral, the compression of spring 24 will be greater than the 75 compressionof spring 25. So it is obvious that,

`(whether in a hypothetical case the equal pressures at ports I1' and I3 be atmospheric and the wards its neutral position and a corresponding movement of fluid from the brake side of reciprocating member 23 to the compressor side. either by seepage past the loose fitting reciprocating member 23, or around by means of a bypass such as 30 in Figure 6. If the static condition of. pressure and ow at ports," and I9 is maintained long enough, reciprocating member 23 will eventually resumeits neutral position, as shown in Figure 2, at which position the compressionsof springs 24 and 25' are again equalized. If the braking pressure is now released, the reciprocating member will be rushed toward the compressor side until projection 29 engages seat 22,v blocking oil further ow of uid'and holding the b ake shoes at their'desired clearance. Y

Thus, it will be seenl that by the .automatic parent that the retracting movement of the actuated brake members is also controlled with the result that the brakes are automatically adjusted by this device to compensate for any deilclency or excess of ,fluid in the lines, without in the least affecting the normal, quick action of the brakes.

It also will be seen that with the liquid volume in the -lines under automatic control at all times, the fluid will tend to illl all voids between the compressor piston and the actuated member, and thereby eliminate the` possibility of air bubbles getting into the lines on the return stroke of l the brake pedal.

Further, it will 'be seen that with the voids fllled in the compressor and the fluid-lines at every instant, it will be p ossible to keep a tight adjustment on the brake pedal with the result that effective work may be done at all stages of the compression stroke when the system is operating under normal conditions.

In case of excessive leakage of fluid or the breakage of one of the fluid lines, the reciprocating member 23 will travel'the complete length of the cylinder I3, as shown ln Fig. 4, thereby eil'ecting a seal and preventing the further movement of liquid into that line.

Although I have hereinbefore set forth the preferred form of my invention, it is understood that certain modiilcations can be made such as shown in Figures 5 and 6. I disclose the use of a double acting spring in Figure 5, instead of two separate/springs. One end of the spring is retained in an annular recess 32 inthe cylinder I3, and the other end ln an annular recess 3,3 in the reciprocating member 23, so that if the member 23 be at any position to the left of that shown in Figure' 5, there will be a compression in the spring tending to force the member 23 to -the right, for example when the device is compensating for a lack of fluid in the brakes 1 and lines-I2. If the member 23 is in any position to the right of the vposition shown in Figure 5, there will be a tension in the spring tending to pull the reciprocating member 23 back to, it; neutral position, for example when'compensating for a surplus of fluid in the brakes '1 and lines I2. In this modification of my invention, one spring can be adapted to perform the'work of. two.

In Figure 6 I disclose the use of a tightly tted reciprocating member 23, together with a bypass 30, constructed within the cylinder I3. In this construction, instead of the fluid seeping around the sides of the loose tting reciprpcatingmember 23, when thesprings 24 and 25 are centralizing it, the fluid/'can now flow around the mem.- ber 23 by means of the bypass 30. This bypass from face to face of reciprocating member 23, or could be a longitudinal groove cut inl either the piston orcyllnder wall to serve the same purpose. Just as long as there is an unobstructed but restricted means for the fluid to get from one side to the other of the reciprocating member 23, my requirements are satisfied. The use of a valve orvalves in this passage or the use of a large passage would render the device useless for the purpose intended.

Various types of springs and spring actions are also contemplated as well as various shapes and combinations of pistons, cylinders, valve seats ,and so forth.

Having described my invention, what I now claim is a.

1. An automatic hydraulic slack adjuster comprising a cylinder, an inlet port in one end of said cylinder, an outlet port in the opposite end of said cylinder, a floatingpiston in said cylinder, relatively weak double acting resilient means tending to move said piston towards a central portion in said cylinder without compromising the action of the fluid on said piston, restricted but could just as Well be a Asmall hole drilled through unobstructed means for permitting the ow of fluid past said piston when said piston is in an unseated position, andvmeans on' said piston for simultaneously closing either of, said ports and stopping the flow of fluid past said piston.

2. In combination with a hydraulic system having a fluid actuating member and fluid actuated member, a device of the character described comprising a cylinder having a -port at each end, said ports communicating respectively with said actuating member and isaid actuated member, a floating piston in said cylinder, relatively .Weak resilient means'tending to move said piston toward a position intermediate the ends of said cylinder without materially aiecting the action of the fluid on said piston, means for `permitting restricted but unobstructed flow of fluid past said piston at all times When said pist0n is in an unseated position, and means on `said piston adapted to contact means-in the port adjacent the actuating member to stop the ow of fluid through said last mentioned port.

3. In combination with afluid system consisting of a fluid actuating member, a fluid actuated member 'and a, uid transfer line connecting said members, an automatic slack adjusting device interposed in said line, comprising a cylinder having means in each end thereof for making connection, to said uid transfer line, a piston in said cylinder, means for providing an unobstructed but restricted fluid by-pass around said piston at all times when said piston is in an unseated position, relatively weak-l double act'- ing springs in said cylinder tending to move said piston `toward a-position intermediate the ends of said cylinder without materially compromising the action of the uid on said piston` and means on said piston arranged to contact means on said cylinder for simultaneously stopping 'the by-pass of flu-id around said piston and effecting a. seal against the ow oilfiuid from the actuated member toward the actuating member ter has been released,

after'the lat- 4, An automatic hydraulic slack adjusting device comprising a cylinder, fluid tight connecftions at the extreme ends of said cylinder, the

primary connection leading to a fluid actuating said piston having a clearance sumcient to permit restricted by-pass 'of uidabout said piston at all times when said piston is in an unseated position, means onvsaid piston adapted to contact means at the primary end of said cylinder tosimultaneously block said by-pass and effect a positive seal' against the return ilow of uid through said 'primary' connection, and vrelatively weak exible means in said cylinder tending to normally maintain said piston in a central 'position in said cylinder Without materially compromising the action of the iuid on said piston.

5. In a fluid system having an actuating and actuated member, an automatic slack adjusting device comprising a valve body, a check valve in said body, a primary connection leading to said actuating member, -a secondary connection leading to said-actuated member, a valve seat between said check valve and said primary connection, an unobstructed yet restricted by-pass around said check valve when the latter is in -an unseated position, and relatively weak -eXf ible means tending to normally maintain said check valve in an unseated position Without mate'rially interfering with the action of the uid on said check valve.

` ARTHUR B. SCI-IULTZ. 

